This is the Eurorack version of my NGF 12dB Multimode VCF.This filter type is widely used in many synthesizers. You can find it in Electronotes or in the SEM modules and in many other synthesizers as well. Nonetheless I have made some changes and adds. I wanted the filter to sound clean with no feedback and the feedback going from soft to very harsh. And usable for pinging (percussion). So I used the the CA3280 for good clean audio (You can use the newly available AS3280 instead). And added a voltage controlled feedback loop going from soft to harsh. This can give the filter a harsh sound and a lot of character. You can adjust the this behavior over a wide range with the calibration trimmers or changing one resistor and capacitor.

Specs and features

• 12dB voltage controlled multimode filter
• Two inputs for easy mixing
• Low pass, high pass, band pass and notch filter output
• Positive and negative ENV control with sign changer
• Temperature compensation with KTY81-110
• CV inputs for linear TM, log TM, envelope, V/Oct tracking and emphasis
• Runs on +/-12V and +/-15V (with minor resistor value changes for best performance)
• Power consumption around 80mA each rail

The documentation and the Gerber files for download can be found in my website.